You know better than me that it's a great singles team. And I guess it could work well in doubles too. Some things:
-I love Discharge, you love Discharge, we're the children of Reborn and spam Discharge in these field effects, but as Fezz also mentioned, Gatr and Hawlucha hate Discharge. If you insist on using it on Jolteon, and if you know or you guess that your opponent will go Doubles, don't Choice her. If you are to go into triples, preferably don't choice her either. In doubles she can spam Specs'd Discharge next to Donphan, P2, ...Roserade resists it and has a passable special bulk, but if you paralyze Fern's First Lady, she's done for.
Same goes for triples, but it's trickier. Sometimes, Jolteon will be fine playing on a wing with one of its good partners at center, and center Pokemon in triples have to take a lot of pressure. But if Jolteon has to be center to hit all three opponents, that means that both Gatr and Hawlucha must come off the bench. But there's also a thing called Wide Guard and will make things really awkward. It will stop Discharge from hitting your opponent, it will make you have to rely on VSwitch, and in multibattles that means getting out of the field and bringing another pokemon that may get hit on the same round, or that may not be optimal to be in the field at that moment but you just were forced to zap with VSwitch because Discharge was blocked by WG.
I'm not telling you "keep DC" or "put TBolt" or "slash VSwitch", I'm just noting some stuff for you to think.
-Fern's First Lady will be almost absent against steel, I think. HP Rock gets it the widest possible SE coverage, I get it, but I think HP Fire is the way to go. Heatran won't be there (bar champion) and I think that the rewards of Fire are bigger. Fire and Flying types will have to deal with your Stab Sludgebomb at least.
-I have a thing: in Singles I'm a proSpin guy. I want MY hazards where they are. That said I think that for this format Defog is the superior options: a) you can use it against the Ghost leader ( a great tactic for Ghost monos against Spin teams is singles, stacking Spikes with Frosslass and TSpikes with Cofagrigus and spamming Hex (or Venoshock) to sweep. Also Defog is great for multibattles: it helps you hit that Stone Miss or Hydro Miss or Focus Miss. And... Defog removes opponent screens. Also pretty good in multibattles. I have no Deffoger to suggest over Donphan, it's just some more food for thought. Damn Gen5 axing Defog and making Defog Poison Heal Gliscor illegal. Damnit damnit damnit. Defog followup to the next point.
-If you manage to stick a Defogger on the team over Donphan, you can also give Hawlucha Drain Punch over Brick Break. Same power, vastly different utility. And since you lack priority, helping Hawlucha to stay healthy longer is good. Also, just noting that right now Hawlucha has real trouble with Aegislash (and Rotom, and Rotom-Fan, Emolga, Zapdos, Thundurus, you get it).
-P2 also has trouble attacking Steel types and more. You will need the most coverage you can get, so perhaps you should ditch one of the two utility slots for something like Tbolt, or Shadow Ball.
In general, I think you may face problems with gyms that have good means of speed control, like TR or Tailwind (or pehaps Swift Swim, if they can dispose Jolteon and Rosa in time)